The invention relates to a screwdriver for handling a screw in the body of a person or an animal, comprising a handle having a stem which is permanently connected to the handle and to whose distal end a screw can be fitted.
A screw driver of this kind is known from U.S. Pat. No. 6,189,422 B1.
For holding the screw at the screwdriver during inserting it into the body, the known screwdriver has a first inner tubular shaft surrounding the stem. The inner shaft has a clamping gripper at its distal end for clamping and holding the screw. A second outer tubular shaft surrounds the inner shaft and is displaceable axially relatively to the inner shaft and relatively to the stem.
In a first position, the outer shaft is displaced in an axial direction to such an extent that the clamping gripper of the inner shaft is pushed radially inwardly thereby clamping the screw attached to the stem. The assembly of the two displaceable shafts is locked in that position via a locking element which is a spring based ball entering into a circumferential groove.
In that position, the screwdriver can be inserted into the body for example via a trokar.
In a second position, the outer tube is displaced proximally to an extent, that the screw comes free from the clamping gripper. The screw is now free for turning it with the stem. In that second position, the assembly of the two shafts is again locked via the locking element.
In a third position, both shafts are moved proximally to an extent that the distal end of the stem protrudes both shafts. The screw can now be released from the stem.
In the third position, the assembly of outer and inner shaft is again locked via the locking element.
A control allows the movement of the two shafts via an outer slider. The slider can be moved only in axial directions between the three axial different displacement positions.
The spring based ball locks the slider in the three positions. When exerting a force on the slider, the ball comes out of the locking position, slides along an axial direction into the axial next locking position. A disadvantage is that if too much force is acted on the slider, it slides from the first position to the third position giving the screw free. This means, the second position is overrun if too much force is acted on the slider.
If that occurs, the screw may be lost in the body without having turned it in.
For assembling and disassembling the screw driver, the slider can be turned about the longitudinal axis giving the two shafts free for removal.
The connection between the slider and the two shafts occurs via two control elements mounted in the slider with laterally projecting pins at the proximal end of the two shafts.
When assembling the screw driver, the two shafts are inserted into the slider, and a turning movement of the slider locks the two shafts at the screw driver.
But, this turning movement of the slider occurs only when assembling or disassembling the screwdriver for cleaning it or for preparing it for a surgery.
During a surgery, the surgeon only performs the axial sliding movements of the slider with the risk of overrunning the intermediate position.
It is therefore an object of the present invention to develop a screwdriver in that the outer tube can be moved into the different displacement positions with respect to the stem and locked in these displacement positions without one or more locking points having to be jumped over.